Đáp án:
Giải thích các bước giải:
`B = 1/3 + 2/3^2 +.............+ 99/3^99 + 100/3^100`
`3B = 1 + 2/3 +.........+ 99/3^98 + 100/3^99`
`3B - B = ( 1 + 2/3 +.........+ 99/3^98 + 100/3^99 ) - ( 1/3 + 2/3^2 +.............+ 99/3^99 + 100/3^100 )`
`2B = 1 + 1/3 + 1/3^2 +...............+ 1/3^98 + 1/3^99 + 100/3^100`
`6B = 3 + 1 + 1/3 +............+ 1/3^97 + 1/3^98 + 100/3^99`
`6B - 2B = ( 3 + 1 + 1/3 +............+ 1/3^97 + 1/3^98 + 100/3^99 ) - ( 1 + 1/3 + 1/3^2 +...............+ 1/3^98 + 1/3^99 + 100/3^100 )`
`4B = 3 + 100/3^99 - 1/3^99 + 100/3^100`
`4B = 3 + 99/3^99 + 100/3^100`
`B = 3/4 + 1/3^99 . ( 99 + 100/3 ) : 4`
`B = 3/4 + 1/3^99 . 397/12 > 3/16`
`→ B > 3/16`
`→ B < 3/16` là không thể
`→` Đề sai
